1. Field of the Invention
The present invention relates to a node apparatus of an optical ring network.
2. Description of the Related Art
In recent years and continuing, the demand for optical networks is increasing along with the growth of Internet traffic. Among the optical networks, an optical network which is able to handle vast amounts of data at high speed in the form of optical signals is drawing attention. Accordingly, there is a demand for a node configuration that efficiently accommodates and provides channels for such optical networks.
FIG. 1 is a drawing showing an exemplary configuration of a conventional optical ring network. This configuration includes nodes 0-1 through 0-8 that are connected in a ring-like manner. Taking redundancy into consideration, the nodes 0-1 through 0-8 are connected by employing two optical transmission lines of an active system and an auxiliary system (See, for example, Japanese Laid-Open Patent Application Nos. 2-199431 and 11-289296).
With reference to FIG. 2, in a case where the optical transmission line connecting node 0-1 and node 0-8 cannot be used due to a fault, such as disconnection, the fault is recovered from by executing the so-called line protection in which a network which is equivalent to the network prior to the fault is generated by returning (turning back) at the faulty end nodes (in this case node 0-1 and node 0-8). In this case, since the faulty end nodes that are to be controlled are only nodes 0-1 and 0-8, a redundant system can be achieved by simple control.
However, with the foregoing scheme, the number of transit nodes and the transmission distance increases upon recovering from the fault. This leads to a problem of transmission loss of optical signals. Particularly, the loss is more significant at an optical add/drop device that executes add/drop of a particular wavelength inside a transit node rather than at a transmission line; thereby resulting in large degradation of a transmission property during fault recovery.